mirror of
https://github.com/systemd/systemd.git
synced 2024-12-05 00:04:02 +08:00
232 lines
11 KiB
XML
232 lines
11 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="sd_bus_track_new" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_bus_track_new</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>sd_bus_track_new</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>sd_bus_track_new</refname>
|
|
<refname>sd_bus_track_ref</refname>
|
|
<refname>sd_bus_track_unref</refname>
|
|
<refname>sd_bus_track_unrefp</refname>
|
|
<refname>sd_bus_track_set_recursive</refname>
|
|
<refname>sd_bus_track_get_recursive</refname>
|
|
<refname>sd_bus_track_get_bus</refname>
|
|
<refname>sd_bus_track_get_userdata</refname>
|
|
<refname>sd_bus_track_set_userdata</refname>
|
|
|
|
<refpurpose>Track bus peers</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_bus_track_new</function></funcdef>
|
|
<paramdef>sd_bus* <parameter>bus</parameter></paramdef>
|
|
<paramdef>sd_bus_track** <parameter>ret</parameter></paramdef>
|
|
<paramdef>sd_bus_track_handler_t <parameter>handler</parameter></paramdef>
|
|
<paramdef>void* <parameter>userdata</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>sd_bus_track *<function>sd_bus_track_ref</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>sd_bus_track *<function>sd_bus_track_unref</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>void <function>sd_bus_track_unrefp</function></funcdef>
|
|
<paramdef>sd_bus_track **<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_bus_track_get_recursive</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_bus_track_set_recursive</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
<paramdef>int <parameter>b</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>sd_bus* <function>sd_bus_track_get_bus</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>void* <function>sd_bus_track_get_userdata</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>void* <function>sd_bus_track_set_userdata</function></funcdef>
|
|
<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
|
|
<paramdef>void *userdata</paramdef>
|
|
</funcprototype>
|
|
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para><function>sd_bus_track_new()</function> creates a new bus peer tracking object. The object is allocated for
|
|
the specified bus, and returned in the <parameter>*ret</parameter> parameter. After use, the object should be freed
|
|
again by dropping the acquired reference with <function>sd_bus_track_unref()</function> (see below). A bus peer
|
|
tracking object may be used to keep track of peers on a specific IPC bus, for cases where peers are making use of
|
|
one or more local objects, in order to control the lifecycle of the local objects and ensure they stay around as
|
|
long as the peers needing them are around, and unreferenced (and possibly destroyed) as soon as all relevant peers
|
|
have vanished. Each bus peer tracking object may be used to track zero, one or more peers add a time. References to
|
|
specific bus peers are added via
|
|
<citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
|
|
<function>sd_bus_track_add_sender()</function>. They may be dropped again via
|
|
<function>sd_bus_track_remove_name()</function> and
|
|
<function>sd_bus_track_remove_sender()</function>. Alternatively, references on peers are removed automatically
|
|
when they disconnect from the bus. If non-<constant>NULL</constant> the <parameter>handler</parameter> may specify
|
|
a function that is invoked whenever the last reference is dropped, regardless whether the reference is dropped
|
|
explicitly via <function>sd_bus_track_remove_name()</function> or implicitly because the peer disconnected from the
|
|
bus. The final argument <parameter>userdata</parameter> may be used to attach a generic user data pointer to the
|
|
object. This pointer is passed to the handler callback when it is invoked.</para>
|
|
|
|
<para><function>sd_bus_track_ref()</function> creates a new reference to a bus peer tracking object. This object
|
|
will not be destroyed until <function>sd_bus_track_unref()</function> has been called as many times plus once
|
|
more. Once the reference count has dropped to zero, the specified object cannot be used anymore, further calls to
|
|
<function>sd_bus_track_ref()</function> or <function>sd_bus_track_unref()</function> on the same object are
|
|
illegal.</para>
|
|
|
|
<para><function>sd_bus_track_unref()</function> destroys a reference to a bus peer tracking object.</para>
|
|
|
|
<para><function>sd_bus_track_unrefp()</function> is similar to <function>sd_bus_track_unref()</function> but takes
|
|
a pointer to a pointer to an <type>sd_bus_track</type> object. This call is useful in conjunction with GCC's and
|
|
LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable
|
|
Attribute</ulink>. Note that this function is defined as inline function.</para>
|
|
|
|
<para><function>sd_bus_track_ref()</function>, <function>sd_bus_track_unref()</function> and
|
|
<function>sd_bus_track_unrefp()</function> execute no operation if the passed in bus peer tracking object is
|
|
<constant>NULL</constant>.</para>
|
|
|
|
<para>Bus peer tracking objects may exist in two modes: by default they operate in non-recursive mode, but may
|
|
optionally be switched into recursive mode. If operating in the default non-recursive mode a peer is either tracked
|
|
or not tracked. In this mode invoking <function>sd_bus_track_add_name()</function> multiple times in a row for the
|
|
same peer is fully equivalent to calling it just once, as the call adds the peer to the set of tracked peers if
|
|
necessary, and executes no operation if the peer is already being tracked. A single invocation of
|
|
<function>sd_bus_track_remove_name()</function> removes the reference on the peer again, regardless how many times
|
|
<function>sd_bus_track_add_name()</function> was called before. If operating in recursive mode, the number of times
|
|
<function>sd_bus_track_add_name()</function> is invoked for the same peer name is counted and
|
|
<function>sd_bus_track_remove_name()</function> must be called the same number of times before the peer is not
|
|
tracked anymore, with the exception when the tracked peer vanishes from the bus, in which case the count is
|
|
irrelevant and the tracking of the specific peer is immediately
|
|
removed. <function>sd_bus_track_get_recursive()</function> may be used to determine whether the bus peer tracking
|
|
object is operating in recursive mode. <function>sd_bus_track_set_recursive()</function> may be used to enable or
|
|
disable recursive mode. By default a bus peer tracking object operates in non-recursive mode, and
|
|
<function>sd_bus_track_get_recursive()</function> for a newly allocated object hence returns a value equal to
|
|
zero. Use <function>sd_bus_track_set_recursive()</function> to enable recursive mode, right after allocation. It
|
|
takes a boolean argument to enable or disable recursive mode. Note that tracking objects for which
|
|
<function>sd_bus_track_add_name()</function> was already invoked at least once (and which hence track already one
|
|
or more peers) may not be switched from recursive to non-recursive mode anymore.</para>
|
|
|
|
<para><function>sd_bus_track_get_bus()</function> returns the bus object the bus peer tracking object belongs
|
|
to. It returns the bus object initially passed to <function>sd_bus_track_new()</function> when the object was
|
|
allocated.</para>
|
|
|
|
<para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer set on the bus peer
|
|
tracking object at the time of creation using <function>sd_bus_track_new()</function> or at a later time, using
|
|
<function>sd_bus_track_set_userdata()</function>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Return Value</title>
|
|
|
|
<para>On success, <function>sd_bus_track_new()</function> and <function>sd_bus_track_set_recursive()</function>
|
|
return 0 or a positive integer. On failure, they return a negative errno-style error code.</para>
|
|
|
|
<para><function>sd_bus_track_ref()</function> always returns the argument.</para>
|
|
|
|
<para><function>sd_bus_track_unref()</function> always returns <constant>NULL</constant>.</para>
|
|
|
|
<para><function>sd_bus_track_get_recursive()</function> returns 0 if non-recursive mode is selected (default), and
|
|
greater than 0 if recursive mode is selected. On failure a negative errno-style error code is returned.</para>
|
|
|
|
<para><function>sd_bus_track_get_bus()</function> returns the bus object associated to the bus peer tracking
|
|
object.</para>
|
|
|
|
<para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer associated with the
|
|
bus peer tracking object. <function>sd_bus_track_set_userdata()</function> returns the previous user data pointer
|
|
set.</para>
|
|
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Reference ownership</title>
|
|
|
|
<para>The <function>sd_bus_track_new()</function> function creates a new object and the caller owns the sole
|
|
reference. When not needed anymore, this reference should be destroyed with
|
|
<function>sd_bus_track_unref()</function>.
|
|
</para>
|
|
|
|
<refsect2>
|
|
<title>Errors</title>
|
|
|
|
<para>Returned errors may indicate the following problems:</para>
|
|
|
|
<variablelist>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EBUSY</constant></term>
|
|
|
|
<listitem><para>Bus peers have already been added to the bus peer tracking object and
|
|
<function>sd_bus_track_set_recursive()</function> was called to change tracking mode.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EINVAL</constant></term>
|
|
|
|
<listitem><para>Specified parameter is invalid
|
|
(<constant>NULL</constant> in case of output
|
|
parameters).</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-ENOMEM</constant></term>
|
|
|
|
<listitem><para>Memory allocation failed.</para></listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" />
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
<citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|